Critical to cerebellar function is a set of five brainstem neuron assemblies (nuclei) collectively referred to as the precerebellar system. These nuclei are responsible for relaying and processing information that flows from the cerebral cortex and spinal cord to the cerebellum. Precerebellar neurons are generated from dorsal neuroepithelium (the rhombic lip) yet settle in ventral aspects of the medulla and pontine brainstem. To reach their final positions, these neurons must migrate long distances across several brain subdivisions filled with densely packed, synaptically-connected neuropile. Thus, research addressing the development of this crucial, yet rarely studied, neural complex should further elucidate mechanisms underlying cell migration in the mature brain, as well as contribute to our understanding of a critical aspect of cerebellar function. Using clonal analysis, serial analysis of gene expression, and recombinase based fate mapping and mutagenesis techniques, the proposed project will focus on the mechanisms by which precerebellar neuronal identity is established within the rhombic lip.